The 33-year-old Ninkovich, who had been absent from training camp for what coach Bill Belichick described as personal reasons, made the announcement at a news conference after the Patriots practiced Sunday morning.
"I know this team is a tremendous football team this year", said Ninkovich, who spent his eight of his 11 NFL seasons in New England.
This story will be updated. There had been growing speculation about Ninkovich's future, as he skipped New England's first three practices this offseason, including Saturday's first day in full pads.
Ninkovich will the be second Patriot to announce his retirement this year. He also had a sack in the Patriots' postseason opener against the Houston Texans.
Ninkovich played in 44.3 percent of the defensive snaps in 2016, which was lower than his norm, in part because he served a four-game suspension to open the season after a positive test for a banned substance he said was from an over-the-counter supplement.
"In closing, everybody out there with a dream, if you have a dream, just give it your best effort, give it everything you've got", he said. Thank you. Hopefully my playing career has taught me a lot. "I hope it was enough", Ninkovich said.